Lecture 5Lecture 5Tectonic Tectonic

LandformsLandforms

Landforms that result from crustal movementsLandforms that result from crustal movementsLandforms with little erosion so "their shape defines a Landforms with little erosion so "their shape defines a

fractured or deformed surface" Bloomfractured or deformed surface" Bloom

Escarpment or "scarp"Escarpment or "scarp"

• Tectonic Scarp: steep slope from differential movement of surface

High angle Normal faults, Tanzania Rift Valley

http://travel.mongabay.com/tanzania/images/tz_elf_0560.html

HW

FWAxial Lake Deposits Soils

Border Fanglomerate

Basaltic Lava Flows

FlatironsFlatirons

• Dissection of scarp ( often a side of a hogback) by many gullies forms triangular facets

http://en.wikipedia.org/wiki/File:Flatirons.jpg

Joints: Fractures – with no movementJoints: Fractures – with no movement

http://www.pbase.com/dougsherman/image/93468807

And on Mars …And on Mars …

Link courtesy Melissa Hansen

Faults 1: Normal FaultsFaults 1: Normal Faults

• Typical of Divergent Margins

• Rift Valleys and Mid-Ocean Ridges

• High-angle and Listric• Horst and Graben

Structure• Hanging wall is down

Divergent Margins Divergent Margins @ MOR, Iceland @ MOR, Iceland

Graben in Graben in Iceland, a Iceland, a subaerially subaerially exposed Mid-exposed Mid-Ocean RidgeOcean Ridge

Source: Simon Fraser/Science Photo Library/Photo Researchers, Inc.

Rift Valley x-secRift Valley x-sec

Origin of Basaltic magma 2

Faults 2: Reverse Fault StructuresFaults 2: Reverse Fault Structures• Typical of Convergent Margins• E.g. Accretionary Wedges (Santa Catalina

Island’s schists) and Fold and Thrust Mountains (Himalayas, Alps, Appalachians)

• Often low-angle thrusts• Hanging wall is up

http://rst.gsfc.nasa.gov/Sect2/05-01_reverse_fault-jyougashima_DSC8766.jpg

Overhanging Block

http://www.flickr.com/photos/mirkazemian/356833099/sizes/o/

Reverse Fault ScarpReverse Fault Scarp

Klippe - Thrust Fault RemnantKlippe - Thrust Fault Remnant

Chief Mountain, a klippe outlier of the Lewis Thrust, Glacier National Park, MT

http://www.pbase.com/dougsherman/image/93469147

A feature of thrust fault terranes. The klippe is the remnant portion of a nappe after erosion.

Faults 3: Transform Transform Faults Faults between between MOR'sMOR's

http://epod.usra.edu/archive/images/wallace_creek_aerial.jpg

Strike-slip fault

Sag pond along San Andreas Sag pond along San Andreas Transform (strike-slip) FaultTransform (strike-slip) Fault

The linear strike-slip feature running across this anaglyph is one of many transform faults in California.  Along it can be seen good examples of off-set streams [and] a shutter ridge .

From Drury, text paraphrased.

Structural Structural Control by Control by

Folds Folds

Overturned folds in the Paleozoic rocks of the Marathon Basin of Texas.  The ridges are controlled by resistant carbonates. 

From Drury, Ch. 4

A Monocline near Cody, Wyoming

Upwarps 1: The Adirondack Mountains Upwarps 1: The Adirondack Mountains of Northern New Yorkof Northern New York

Source: Clyde H. Smith/Allstock/Tony Stone Images

Mantle upwelling, Upwarp Mountains

Although the rocks are ancient, the uplift that formed the Adirondack dome has occurred within the last 5 million years — relatively recent in geologic time — and is ongoing.

Upheaval Dome, CanyonlandsUpheaval Dome, Canyonlands

http://www.pbase.com/dougsherman/image/93400984

Colorado Plateau Uplift

Salt Dome

Low density Buoyant Salt Diapirs

Surrounding sediments upwarped

Petroleum exploration

Salt Creek Graben at Arches National Park, UT. Salt Creek Graben at Arches National Park, UT. Solution of evaporites in the underlying Pennsylvanian Solution of evaporites in the underlying Pennsylvanian Paradox Fm. caused the Graben to form.Paradox Fm. caused the Graben to form.

A collapse downwarpA collapse downwarp

A Rhyolitic Igneous Dome, Yellowstone CalderaPlumes under Continent Interiors.

Mars: frost heave?Mars: frost heave?

Link courtesy Melissa Hansen

Mounds S. of Elysium Planitia a few kilometers in diameter about 60 meters tall. Fractures suggest mounds formed by uplift

Uplift is not uniform mounds are probably solidified lava.

Mounds contiguous with and texturally similar to flood lavas over Elysium Planitia.

Where dilation cracks provide cross-sectional exposure, the uplifted material is rocky.

Frost heave on a huge scale?

A 2005 photo of Elysium Planitia by the Mars Express spacecraft shows what may be ash-covered water ice. The volume of ice is estimated to be 800 by 900 kilometers in size and 45 meters deep, similar in size and depth to the

North Sea.

Review of Cenozoic TectonicsReview of Cenozoic Tectonics

http://www.globalchange.umich.edu/Ben/Helvetic%20Morcles%20nappe.JPG

A nappe is a large sheetlike body of rock that has been moved more than 2 km (1.2 miles) from its original position. Nappes form during continental plate collisions, when folds are sheared so much that they fold back over on themselves and break apart. The resulting structure is a large-scale recumbent fold. The term stems from the French word for tablecloth.

• Cenozoic Orogenic activity concentrated in two areas– Alpine-Himalayan belt deformation began in the Mesozoic and remains

geologically active. Isolation of Tethys to form the modern Mediterranean Sea

– circum-Pacific belt deformation occurred throughout the Cenozoic

Arabian-African RiftArabian-African Rift1. The underside of Europe collided with numerous microplates rifted from Africa Closing of the Tethys Sea between late Mesozoic and early Cenozoic time4. Thrusts not Subduction3. Messinian Salinity Crisis ~ 5.5 mya

2. Pliocene three way rift.

3. Arabia Microcontinent collision -> Zagros Mts

Subduction-Zone FeaturesSubduction-Zone FeaturesNote sequence from land to trench

If a continent converges from the left, what rocks will fold in the collision? Himalayas

Note ocean plate rocks that don’t get subducted in a collision

• Abyssal plains

– Can be sites of thick accumulations of sediment

– Sediments thickest away from MOR

– Abyssal plains found in all oceans

– Studded by old cold seamounts and MORs

TrenchAccretionary wedgeFore-Arc BasinVolcanic Arc

Back-Arc Basin

Continent

http://www.geol-alp.com/chartreuse/3_tecto_chartreuse/1_ch_occ.html

New Orogen, Nappes still visible

Drawings of Nappes in the Alps

"A spectacular thrust fault in the Caledonides of NW Scotland, which drove Archaean gneisses over Cambro-Ordovician sediments.  The thrust plane is marked by the pronounced bench on the peninsula, which is coated with mylonite.  The typical knobbly topography of the heavily glaciated gneisses is quite obvious in the upper part …. "

From Drury, Ch. 4

Definition Nappes previous slide

Himalayan OrogenyHimalayan Orogeny

Partly subducted so under AW

Subduction and TST

Himalayan OrogenyHimalayan Orogeny

AW

FAB

Fold and Thrust Mountains, Himalayas, Continent-Continent collision

Rain Shadow Desert: Tibetan Plateau

North

INDIA under cloud cover

Taklamakan DesertTaklamakan Desert

Tibetan PlateauTibetan Plateau

Himalayas

Himalayas

NORTHNORTH

San Andreas TransformSan Andreas Transform

Changed Orientation 15 mya SAF forms

MOR Subducted!

North American Cordillera TopographyNorth American Cordillera Topography

Basin and RangeCrust very thin there

Columbia River BasaltsWHY SO FAR INLAND?

Tertiary Tectonic EventsTertiary Tectonic Events

K-T Laramide Continental OverrideBuoyant Subduction

North American Cordillera

Rockies: Buoyant Subduction caused Laramide OrogenyRockies: Buoyant Subduction caused Laramide Orogeny

Normal, thin-skinned

Vertical block uplift

Approaching Continent pushesaccretionary wedge sediments

into forearc sediments

The Grand Tetons in WyomingThe Grand Tetons in Wyoming

Source: Peter French/DRK Photo

High Angle Faults, Buoyant Subduction.

Later origin of Fault Block Mountains Later origin of Fault Block Mountains “Basin and Range” “Basin and Range”

Southwestern North AmericaSouthwestern North America

Huge divergent zone, Basin and Range, not so far inland as Rockies, more normal subduction dip resumes, partial melting in mantle, magma rises similar to rift valley.

But why so Wide? Breakup of flatbuoyantly subducted Farallon Plate?

Basin and Range provinceBasin and Range province

Extensional Featurew/ Normal Faults

BasinRange

Rift vs. Basin and RangeRift vs. Basin and Range

Mirror symmetry, radial cracks about center, divergence, normal faults

Conjugate shear fractures, divergence, normal faults

Displaced terranes – Western CordilleraDisplaced terranes – Western Cordillera

These terranes overlap in age but have different rock types, paleolatitudes and fossils. However, we can deduce when they accreted from their order, and the metamorphic ages of their suture zones

Columbia River BasaltsColumbia River Basalts(including the Saddle Mountains Basalt)(including the Saddle Mountains Basalt)

17my

Columbia River Basalts and Columbia River Basalts and Yellowstone PlumeYellowstone Plume

http://en.wikipedia.org/wiki/Columbia_River_Basalt_Group